In biological objects that are autofluorescent, or have been labelled with fluorescent probes, a frequent requirement is to extract multi-spectral component images from the object that permit the spatial relationships between the variously labelled components to be studied. Living biological objects contain dynamic processes that may be fluorescently labelled so that, by repeating the same multi-spectral scan of the object, the temporal dynamics of these processes may also be studied. In all of these types of experiments it is important to have the ability to rapidly switch excitation wavelengths during the scanning process and the invention aims at providing a method of achieving fast multi-wavelength scanning in an acousto-optical deflector based laser confocal scanning microscope providing fast multi-wavelength scanning.